The subject matter of the present invention relates generally to apparatus for mixing particulate material and in particular to such a mixing apparatus employing a plurality of different shaped blades having multiple functions, including mixing, deflecting, scraping and impelling. The present mixing apparatus outwardly deflects and thorougly mixes two different materials rapidly as the materials move downward through a mixing chamber, scrapes the mixed material from the surface of the chamber, and impels the mixed material through a discharge opening at the bottom of such chamber. As a result the mixing apparatus is capable of continuous flow operation for high speed production of mixed material.
The invention is particularly useful in the manufacture of sand molds and cores employed to cast metal objects, for supplying to mold or core forming boxes a mixture of a first material consisting of sand and resin binder and a second material consisting of sand and catalyst for accelerating the curing and cold setting of such binder. These two materials are fed separately into two inlets in the top of the mixing chamber where they are thoroughly and rapidly mixed before being discharged into mold boxes or mold cores where the binder hardens and sets the mixed material to form the molds and cores used for casting.
The mixing apparatus of the present invention is an improvement on the apparatus shown in U.S. Pat. No. 3,934,858 of R. A. Parsonage, granted Jan. 27, 1976. This prior mixing apparatus employs mixing and deflector blades which extend as one solid piece from the central rotating support shaft to their outer edge so that mixed material tends to build up on and adhere to the surfaces of such blades due to their greater area. In addition, the side wall of the mixing chamber is a conical wall which slopes downward and inwardly so that there is also build up of the mixed material on such walls which is not scraped off of the walls by the blades. The mixing apparatus of the present invention overcomes these problems by employing narrow mixing blades which are attached by spaced support rods to the rotating central shaft, including longitudinal mixing blades whose radial width is less than its thickness and which extend along substantially the entire length of the cylindrical inner surface of the side of the mixing chamber to scrape material from such inner surface. Convoluted mixing blades which spiral downward and inward are positioned with the conical bottom portion of the mixing chamber, which also act as impellers, to move the mixed material through the discharge opening, and as scrapers to scrape the conical inner surface of the bottom portion of the mixing chamber. This is an improvement over the longitudinal blades used to scrape the mixing chambers in the continuous mixing apparatus of copending U.S. Pat. application Ser. No. 595,042 of R. A. Parsonage, filed July 11, 1975, and the batch mixing apparatus of U.S. Pat. No. 3,779,520 of A. Edwards, granted Dec. 18, 1973, which is emptied by compressed air. It should be noted that convoluted mixing blades have been used in other mixing apparatus, such as that of E. D. Abraham, shown in U.S. Pat. No. 3,494,412, granted Feb. 10, 1970, and U.S. Pat. No. 3,637,191, granted Jan. 25, 1972, and of E. A. F. Presser, disclosed in U.S. Pat. No. 2,390,460, granted Dec. 4, 1945, but they do not spiral downward and inward adjacent the conical inner surface of the bottom portion of a mixing chamber so that they can perform the three functions of mixing, impelling, and scraping in the manner of the present invention.
In one embodiment, the mixing apparatus of the present invention supplied 800 pounds of mixed material per minute through the discharge opening while employing a mixture of about 97.9% silica sand of 50 to 75 AFS particle size, a synthetic resin binder of about 1.75% and the remaining 0.35% being catalyst for such binder, the above percentages being given by weight.